Preview brake controlling apparatus and method for automotive vehicle

ABSTRACT

In preview brake controlling apparatus and method for an automotive vehicle, a relative distance of the vehicle to an object for the vehicle to be braked is detected, a determination of whether the vehicle is approaching to the object on the basis of the relative distance of the vehicle to the object is made, a vehicular velocity variation rate (acceleration/deceleration) manipulation variable is made, the determination of whether the vehicle falls in a preliminary brake pressure application enabled state requiring a preliminary brake pressure application on the basis of results of detection at the steps of the approaching state detecting and of the vehicular velocity variation rate manipulation situation detection is made, and a predetermined constant brake pressure in accordance with a vehicular running condition prior to a vehicular driver&#39;s brake manipulation is developed when determining that the vehicle falls in the brake preliminary application enabled state.

BACKGROUND OF THE INVENTION

[0001] a) Field of the Invention

[0002] The present invention relates to preview brake controllingapparatus and method in which a brake pressure during an automaticcontrol process is set in an automotive vehicle when a front obstacle tobe braked is detected.

[0003] b) Description of the Related Art

[0004] A Japanese Patent Application First Publication No. Heisei7-144588 published on Jun. 6, 1995 exemplifies a first previouslyproposed collision preventing apparatus for an automotive vehicle inwhich an automatic brake control is effected so that a collision betweena front obstacle and the vehicle is previously prevented from occurringwhen a distance between the front obstacle and the vehicle does notsatisfy a predetermined distance.

[0005] A Japanese Patent Application First Publication No. Heisei6-24302 published on Feb. 1, 1994 exemplifies a second previouslyproposed automatic preliminary braking system in which a heel detectorto detect a heel of a driver's foot which is rested on a heel rest isused to detect an accelerator manipulation information which isdifferent according to different drivers and before the brakemanipulation a preliminary brake pressure is applied.

SUMMARY OF THE INVENTION

[0006] In each of the first and second previously proposed collisionpreventing and automatic preliminary brake pressure apparatuses, a lowerbrake pressure of the automatic (preliminary) brake in a state where thevehicle is approaching to the obstacle gives an effect on a shortage ina free running distance or on an improvement in a responsivecharacteristic when the driver depresses a brake pedal. However, thereis a possibility that the automatic brake control is effected in a casewhere depending upon an accuracy of an inter-vehicle distance sensor, anobject other than the front obstacle on the same traffic lane is and afrequency of manipulating depressions-and-releases on an acceleratorpedal is high. In this case, a deceleration developed due to the effectof the automatic brake control often gives the driver an unpleasant (oruncomfortable) feeling.

[0007] On the contrary, it is considered that the set automatic(preliminary) brake pressure may be set to be lower. However, theactually developed vehicular deceleration may be larger than a targetvalue thereof due to a control accuracy of a brake liquid pressurecontrol actuator, a vehicular weight, or a variation in a frictionalcoefficient of the road surface on which the vehicle is running.

[0008] In this case, the application of the automatic (preliminary)brake pressure often gives the driver unpleasant (or uncomfortable)feeling.

[0009] It is, therefore, an object to provide preview brake controllingapparatus and method which can provide a preview brake control withoutgiving a vehicular driver unpleasant feeling by activating a preliminarybrake pressure during an automatic control process even if a vehiculardeceleration equal to or higher than a target value thereof occurs.

[0010] According to one aspect of the present invention, there isprovided with a preview brake controlling apparatus for an automotivevehicle, comprising: an object detector to detect a relative distance ofthe vehicle to an object for the vehicle to be braked; an approachingstate detector to detect whether the vehicle is approaching to theobject on the basis of the relative distance of the vehicle to theobject; a vehicular velocity variation rate manipulation situationdetector to detect a manipulation situation on a vehicular velocityvariation rate; a preliminary brake pressure application startdetermining section that determines whether the vehicle falls in apreliminary brake pressure application enabled state requiring apreliminary brake pressure application on the basis of detection resultsby the approaching state detector and by the vehicular velocityvariation rate manipulation situation detector; and a brake pressuregenerator to develop a predetermined minute brake pressure in accordancewith a vehicular running condition prior to a vehicular driver's brakemanipulation when the preliminary brake pressure application startdetermining section determines that the vehicle falls in the preliminarybrake pressure application enabled state.

[0011] According to another aspect of the present invention, there isprovided with a preview brake controlling method for an automotivevehicle, comprising: detecting a relative distance of the vehicle to anobject for the vehicle to be braked; detecting whether the vehicle isapproaching to the object on the basis of the relative distance of thevehicle to the object; detecting a vehicular velocity variation ratemanipulation situation; determining whether the vehicle falls in apreliminary brake pressure application enabled state requiring apreliminary brake pressure application on the basis of detection resultsat the steps of the approaching state detecting and of the vehicularvelocity variation rate manipulation situation; and developing apredetermined constant brake pressure in accordance with a vehicularrunning condition prior to a vehicular driver's brake manipulation whendetermining that the vehicle falls in the brake preliminary applicationstate.

[0012] This summary of the invention does not necessarily describe allnecessary features so that the invention may also be a sub-combinationof these described features.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1A is a system configuration view representing a firstpreferred embodiment of the preview brake controlling apparatus for anautomotive vehicle.

[0014]FIG. 1B is a circuit block diagram of a controller 29 shown inFIG. 1A.

[0015]FIG. 2 is a cross sectional view of an electronic vacuum pressurebooster to which the preview brake controlling apparatus in the firstembodiment shown in FIG. 1A is applicable.

[0016]FIG. 3 is an operational flowchart representing a controlprocedure executed by the preview brake controlling apparatus shown inFIGS. 1A and 1B.

[0017]FIG. 4 is a characteristic graph representing a preliminary brakepressure calculation map.

[0018]FIG. 5 is an operational flowchart representing a processingflowchart of a preliminary pressure determining procedure in a controlprocedure in FIG. 3.

[0019]FIG. 6 is an operational flowchart representing one example of asubroutine in an operation determination process (step S14) shown inFIG. 5.

[0020]FIG. 7 is a characteristic graph of a calculation map of athreshold value of accelerator depression determination representing arelationship between a vehicular velocity and the threshold value ofaccelerator depression determination with a transmission shift positionas a parameter.

[0021]FIGS. 8A, 8B, and 8C are explanatory views for explaining acalculation map of the accelerator depression determination thresholdvalue.

[0022]FIG. 9 is a characteristic graph representing a vehicular velocityand a threshold value at which an accelerator releasing speed isdetermined.

[0023]FIGS. 10A, 10B, 10C, and 10D are integrally a timing chart forexplaining an operation of the preview brake controlling apparatus inthe first preferred embodiment.

[0024]FIG. 11 is a system configuration view representing a secondpreferred embodiment of the preview brake controlling apparatusaccording to the present invention.

[0025]FIG. 12 is an operational flowchart representing one example of anoperation determination procedure in the second preferred embodiment ofthe preview brake controlling apparatus according to the presentinvention shown in FIG. 11.

[0026]FIG. 13 is a characteristic graph representing the vehicularvelocity and the threshold value of accelerator depression determinationin the second preferred embodiment shown in FIG. 11.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] Reference will hereinafter be made to the drawings in order tofacilitate a better understanding of the present invention.

[0028] (First Embodiment)

[0029]FIG. 1A shows a system configuration view representing a firstpreferred embodiment of a preview brake controlling apparatus accordingto the present invention.

[0030] In FIG. 1A, reference numerals 21FL and 21FR denote front leftand right road wheels of the vehicle and 21RL and 21RR denote rear leftand right road wheels of the vehicle.

[0031] Each brake actuator 22FL through 22RR is constituted bydeveloping a braking force in accordance with a braking pressure to besupplied.

[0032] Each brake actuator 22FL through 22RR is linked to a mastercylinder 25 via an electronic vacuum pressure booster 24.

[0033] The electronic vacuum pressure booster 24 is constituted by FIG.2. That is to say, a diaphragm 14 is defined with a pressure variationchamber 1 and a vacuum pressure chamber 2. The pressure variationchamber 1 provides a vacuum pressure state determined according to anengine vacuum pressure when the brake is not effected so that a pressurebalanced state occurs with respect to the vacuum pressure chamber 2.When the brake is operated, the atmospheric pressure is introduced sothat a pressure difference to the vacuum pressure chamber 2 occurs. Amultiplied weight is transmitted to the master cylinder 25. The vacuumpressure chamber 2 is always maintained at a vacuum pressure during anengine start.

[0034] An axial envelope 17 is fixed on a center part of the diaphragm14. A communication passage 11 to communicate between the vacuumpressure chamber 2 and the pressure variation chamber 1 is formed. Avacuum valve 3 is disposed on a right end sided opening of thecommunication passage 11. The vacuum valve 3 is closed when the driverstrokes the brake pedal 23 or an electromagnetic valve 5 is energized sothat the communication between the vacuum pressure chamber 2 andpressure variation chamber 1 is interrupted.

[0035] In addition, an atmospheric valve 4 is interposed between thepressure variation chamber 1 and the air to cooperate with a valve body12 formed on a slidable envelope 5 b as will be described later so as tobe open when the driver depresses a brake pedal 23 to be stroked or theelectromagnetic valve 5 is energized, thus the air being introduced intothe pressure variation chamber 1.

[0036] The electromagnetic valve 5 includes a solenoid 5 a disposed inan inner periphery of the axial envelope 17 and the slidable envelope 5b opposed to the solenoid 5 a. An engagement portion 18 is formed on aright end of the slidable envelope 5 b.

[0037] The slidable envelope 5 b is biased in the rightward direction bymeans of a return spring 15 disposed within the vacuum pressure chamber2.

[0038] An operating rod 6 is disposed within an inside of the slidableenvelope 5 b and a tip thereof is linked to a master cylinder 25 via apush rod 8. Return springs 13 a and 13 b are disposed within an axialenvelope 17, a vacuum valve 3, and the atmospheric pressure valve 4 anda return spring 16 is interposed between the operating rod 16 and theslidable rod 5 b.

[0039] Referring back to FIG. 1A, the brake pedal 23 is attached ontothe operating rod 6 of the electronic vacuum booster 24. A brake switch26 to detect a depression of the driver on the brake pedal 23 isdisposed therein.

[0040] On the other hand, an accelerator opening angle sensor 28 isdisposed on an accelerator pedal 27 to detect a depression variable ofthe accelerator pedal 27.

[0041] Furthermore, a brake pressure sensor 33 is disposed on an outputpipe of the master cylinder 25 to detect a brake pressure.

[0042] A controller 29 controls the electromagnetic valve 5 of theelectronic vacuum booster 24.

[0043] The controller 29 inputs various detection signals, viz., aswitch signal from the brake switch 26, an accelerator opening angle θof the accelerator opening angle sensor 28, and brake pressure of thebrake pressure sensor 33, a vehicular velocity signal V of the vehicularvelocity sensor 30 to detect the vehicular velocity, the vehicularvelocity sensor 30 including road wheel velocity sensors, aninter-vehicle distance L of an inter-vehicle distance sensor 31constituted by a laser radar or a millimetric wave radar, and a shiftposition signal of a shift position sensor 36 to detect a range positionof an automatic transmission AT selected by the driver.

[0044] Then, the controller 29 controls a braking force to control theelectromagnetic valve 5 of the electronic vacuum booster 24 on the basisof inputted various sensor signals described above.

[0045]FIG. 1B shows a general circuit block diagram of the controller29.

[0046] As shown in FIG. 1B, the controller 29 includes a microcomputerhaving a CPU (Central Processing Unit) 29 a, a ROM (Read Only Memory) 29b, a RAM (Random Access Memory) 29 c, an Input Port 29 d, and an OutputPort 29 e.

[0047]FIG. 3 shows an operational flowchart to be executed by thecontroller 29. The routine shown in FIG. 3 is executed as a timerinterrupt routine for each predetermined period of time (for example, 10milliseconds).

[0048] It is noted that each control flag and each variable shown in theflowchart shown in FIG. 3 are reset to zero in an initialization.

[0049] At a step S1, controller 29 reads the switch signal from thebrake switch 26 and determines whether the switch signal indicates an ONstate, viz., whether brake switch 26 is turned on so that the driverdepresses brake pedal 23.

[0050] If the brake pedal 23 is depressed (Yes) at the step S1, theroutine goes to a step S2.

[0051] At step S2, controller 29 reads vehicular velocity signal V fromvehicular velocity sensor 30 to determine if vehicular velocity V iszero, viz., the vehicle has stopped. If V=0 (Yes) (namely, the vehiclestops) S2, the routine goes to a step S3. If V>0 (No) at step S2(namely, the vehicle is running), the routine jumps to step S4.

[0052] At step S3, controller 29 reads a vehicular weight m detected byweight sensor 32 and the routine goes to a step S4.

[0053] At step S4, controller 29 sets a preliminary brake pressure Pstto zero and the routine goes to a step S5.

[0054] At step S5, controller 29 controls electromagnetic valve 5 tonon-power supplied state so that the preliminary brake pressure Pstdeveloped at the master cylinder 25 is zeroed. Then, the present timerinterrupt routine is ended and is returned to a predetermined mainroutine.

[0055] On the other hand, if brake switch 26 is turned off, controller29 determines that brake pedal 23 is released and routine goes to a stepS6 to determine if it is necessary to develop the preliminary brakepressure, viz. , to execute a preliminary brake pressure determiningprocess (refer to FIG. 5).

[0056] Next, at a step S7, controller 29 determines if it is necessaryto develop the preliminary brake pressure on the basis of a status of acontrol operation flag Fc determined in the preliminary pressuredetermining process at step S6.

[0057] If controller 29 determines that it is not necessary to developthe preliminary brake pressure since Fc=0 at step S7 (No), the routinejumps to step S4 described above.

[0058] If controller 29 determines that it is necessary to develop thepreliminary brake pressure according to the status of the controloperation flag (Fc=1) at step S7 (Yes), the routine goes to a step S8.

[0059] At step S8, controller 29 reads a preliminary brake pressurestart vehicular velocity V0 which is the vehicular velocity at a time ofstart of the preliminary brake pressure. At step S9, controller 29 setspreliminary brake pressure Pst. This setting of preliminary brakepressure Pst is carried out by referring to a preliminary brake pressurecalculation map shown in FIG. 4 on the basis of preliminary pressurestart vehicular velocity V0 and vehicular weight m measured at the timeof the vehicular stop at step S3.

[0060]FIG. 4 shows the preliminary brake pressure calculation maprepresenting a relationship between vehicular velocity V and a set valueof the preliminary brake pressure Pst during an automatic control.

[0061] As the vehicular velocity V0 becomes higher when it becomesnecessary to develop the preliminary brake pressure, a vehiculardeceleration that the driver feels is small although the brake pressurevalue is the same, As the vehicular velocity V0 described above is slow,this driver's feeling on the vehicular deceleration is relatively large.With these in mind, a characteristic curve is set such that a lowvehicular velocity range A1 has a constant minimum value Pmin, a highvehicular velocity range A2 has a constant maximum value Pmax, and alinear interpolation between the minimum value Pmin and the maximumvalue Pmax is taken in a middle velocity range A2.

[0062] Furthermore, the setting pressure is corrected to be higher sincea correction of the setting pressure is carried out in accordance withvehicular weight m and as vehicular weight is increased, the effect ofbrake pressure is small.

[0063] Next, at step S10, controller 29 reads brake pressure Pb detectedby brake pressure sensor 33.

[0064] A power supply control is carried out by controller 29 forelectromagnetic valve 5 so that the brake pressure Pb becomes coincidentwith preliminary brake pressure Pst and timer interrupt routine is endedand is returned to the predetermined main routine.

[0065]FIG. 5 shows a flowchart of a subroutine called at step S6 shownin FIG. 3.

[0066] As shown in FIG. 5, controller 29 reads the detection signal andthe switch signal of each kind of sensors at step S11.

[0067] At a step S12, controller 29 calculates an approaching distanceL0 to determine if the vehicle is approaching to an object to be brakedsuch as a preceding vehicle running ahead of the vehicle at a slowervelocity than the vehicle, a preceding vehicle stopped in front of thevehicle, or an obstacle on a front road surface in accordance with anequation (1).

[0068] It is noted that X in equation (1) denotes a deceleration (G). Inaddition, dV denotes a relative velocity of the vehicle to the objectand is a differential value of the inter-vehicle distance (variationrate in the inter-vehicle distance) which is a deviation between presentinter-vehicle distance L(n) and previously read inter-vehicle distanceL(n−1) detected by inter-vehicle distance sensor 31 divided by the timerinterrupt period T.

L0={V ²−(V−dV)²}/(2*X*9.8)  (1)

[0069] Next, at a step S13, controller 29 determines if the presentinter-vehicle distance L(n) is smaller than the approaching distance L0.If L(n)≧L0 (No) at step S13, the routine goes to a step S19 sincecontroller 29 determines that the vehicle is not approaching to thefront object.

[0070] If L(n)<L0 (Yes) at step S19, the routine goes to step S14 sincecontroller 29 determines that the vehicle is approaching the frontobject.

[0071] At step S14, controller 29 executes a subroutine of the operationdetermining process of the preliminary brake pressure on the basis ofoperation situation of the accelerator pedal.

[0072] This operation determining process sets the threshold value θSETto detect a development situation of acceleration from a depressed stateof accelerator pedal 27.

[0073]FIG. 6 shows the subroutine of preliminary brake pressureoperation determining process at step S14 in FIG. 5.

[0074] In details, at a step S21, controller 29 sets a depressiondetermination threshold value θSET to detect a development situation ofa vehicular acceleration according to a depression state of theaccelerator pedal 27. The setting of the depression determinationthreshold value θSET is carried out by referring to the depressiondetermining threshold value calculation map shown in FIG. 7 on the basisof the vehicular velocity V from the vehicular velocity sensor 30 andthe shift position signal from the shift position sensor 36.

[0075] The depression determining threshold value calculation map is arepresentation of a relationship between the vehicular velocity V andthe depression determination threshold value θSET, as shown in FIG. 7,with the shift position of automatic transmission AT as a parameter. Thedepression determining threshold value θSET is set to a value whichenables to be deemed that neither a sudden braking feeling nor anunpleasant feeling is given to the driver even if the preliminary brakepressure is applied in a case where an engine braking is acted upon whenthe driver releases the accelerator pedal 27 from the deep depressionstate.

[0076] In a case of the sudden operation of the preliminary brakepressure during the run of the vehicle, a condition such that neithersudden brake operation feeling nor unpleasant feeling are given to thedriver can include as shown in FIG. 8A.

[0077] In details, instantly when the driver returns the depressedaccelerator pedal 27 to a substantially original position from a statein which the driver has depressed the accelerator pedal 27 to acceleratethe vehicle or to cruise the vehicle at a constant velocity (cruiserun), the engine brake is usually acted upon the vehicle. In thisaddition, if the preliminary brake pressure is acted upon the vehicle, agenerated deceleration with the preliminary brake pressure is overlappedover the engine brake deceleration.

[0078] In this case, in order not to give the driver unpleasant feelingnor uncomfortable feeling, it is desirable to reduce a ratio of adifference, i.e., ΔG1/ΔG2 to be equal to or lower than a predeterminedvalue Gd(ΔG1/ΔG2 Gα). The one difference ΔG1 is a difference between theacceleration at which the vehicle is running or the vehicle cruises andthat at which both of the engine brake and the preliminary brakepressure are acted upon the vehicle, as shown in FIG. 8A. The otherdifference ΔG2 is a difference between the acceleration at which thevehicle is running or the vehicle cruises and that at which only theengine brake is acted upon the vehicle, as shown in FIG. 8A.

[0079] At this time, as shown in FIG. 8B, since the deceleration ΔEwhich can be achieved by means of the engine brake during the lowvelocity region is smaller than that which can be achieved therebyduring the high velocity region, it is necessary to enlarge theacceleration G before the return of the accelerator pedal 27 to theoriginal position as compared with the case of the high velocity regionin order to reduce the ratio ΔG1/ΔG2 to be equal to or lower than thepredetermined value of ΔGα. To achieve this, it is necessary to make adepression variable of the accelerator pedal 27 at the low velocityregion larger than that at the high velocity region.

[0080] In addition, a magnitude of acceleration with respect to thedepression variable of accelerator pedal 27 when the shift position ofautomatic transmission AT is higher, viz., a transmission gear ratio issmaller is smaller than that when the shift position of automatictransmission AT is lower, viz., the transmission gear ratio is larger.

[0081] Hence, as shown in FIG. 7, the characteristic curve is set tohave the constant maximum value θmax at the low velocity region B1 whichis equal to or lower than a city street running velocity (corresponds toabout 40 Km/h), to have the constant minimum value θmin at the highvelocity region B3 which is equal to or higher than a free-way runningvelocity (corresponds to about 80 Km/h), and to have a linearinterpolation value between the maximum and minimum value θmax and θminat a middle velocity region B2. Furthermore, since the magnitude ofacceleration with respect to the depression variable of the acceleratorpedal 27 becomes smaller as the gear shift position of automatictransmission AT becomes smaller (viz., the gear ratio of automatictransmission AT becomes smaller), the correction of the threshold valuein the characteristic curve of FIG. 7 is carried out in accordance withthe shift position of automatic transmission AT. If a minimum gear ratioshift position is 1F and a maximum gear ratio shift position is 4F, thethreshold value of θSET becomes higher as the shift position ofautomatic transmission AT becomes higher.

[0082] As described above, if the depression determining threshold valueθSET is set at step S21, the routine shown in FIG. 6 goes to a step S22.

[0083] At step S22, controller 29 determines if the accelerator openingangle θ from accelerator opening angle sensor 28 is wider than theaccelerator depression determining threshold value of θSET set at stepS21.

[0084] If θ>θSET (Yes) at step S22, the routine goes to a step S23 inwhich a depression flag F_(SET)(n) is set to F_(SET)(n)=1.

[0085] After an initialization at the next step S24, the routine goes toa step S26.

[0086] The initialization of step S24 is carried out in such a mannerthat an accelerator return start opening angle θREL is set to zero(θREL=0), a return counter C_(REL) is set to zero (C_(REL)=0), a returnflag F_(OFF) is reset to zero (F_(OFF)=0), and an operation enable flagF_(PBS) is reset to zero (F_(PBS)=0).

[0087] On the other hand, if, at step S22, θ≦θSET (No), the routinejumps to a step S25 in which the depression confirmation flag F_(SET)(n)is set to 0 (F_(SET)=0). Then, the routine goes to step S26.

[0088] At step S26, controller 29 determines if a previously storedprevious depression confirmation flag F_(SET)(n−1) is 1 (F_(SET)(n−1)=1)and the present depression confirmation flag F_(SET)(n) is 0(F_(SET)(n)=0) (logical AND).

[0089] If F_(SET)(n−1)=1 and F_(SET)(n)=0 (Yes) at step S26, the routinegoes to a step S27.

[0090] If F_(SET)(n−1)≠1 and F_(SET)(n)≠0 (No) at step S26, the routinejumps to a step S29.

[0091] At step S27, the return flag F_(OFF) is set to 1 (F_(OFF)=1) andthe return start opening angle θREL=0. Then, the routine goes to a stepS28.

[0092] At step S28, controller 29 sets the threshold value dθSET of adepression return velocity by referring to a depression return velocitycalculation map shown in FIG. 9 and vehicular velocity V of the vehicle.

[0093] Thereafter, the routine goes to a step S29.

[0094]FIG. 9 shows the calculation map of the accelerator depressionreleasing velocity threshold value of dθSET corresponding to thevehicular velocity V. This threshold value of dθSET is set to a valuewhich can be predicted from the fact that the driver would transfer fromthe release of accelerator pedal 27 to the depression of brake pedal 23according to a return velocity of accelerator pedal by the driver.

[0095] In details, for example, as shown in FIG. 9, the characteristiccurve is set to have the constant maximum value dθmax when the vehicularvelocity V falls in the low velocity region such as the city street runC1 (corresponds to about 40 Km/h or lower), to have the constant minimumvalue dθmin at the high velocity region such as the freeway run C3(corresponds to about 80 Km/h or higher), and to have the linearinterpolation value between the maximum and minimum values dθmin anddθmax at the middle velocity region C2.

[0096] At step S29, controller 29 determines if the return flag F_(OFF)is set to 1 (F_(OFF)=1).

[0097] If F_(OFF)=1 (Yes) at step S29, the routine goes to a step S31.

[0098] If F_(OFF)=0 (No) at step S29, the routine goes to a step S30.

[0099] At step S31, controller 29 increments return counter C_(REL) byone (C_(REL)=C_(REL)+1).

[0100] At the next step S32, controller 29 determines if the acceleratoropening angle θ is narrower than a previously set return opening anglethreshold value θCLEAR which enables to be deemed that the opening angleof accelerator pedal 27 is the release opening angle.

[0101] If θ<θCLEAR (Yes) at step S32, the routine goes to a step S33.

[0102] At step S33, controller 29 sets the return flag F_(OFF) to zero(F_(OFF)=0) and the routine goes to a step S34.

[0103] At step S34, controller 29 calculates an accelerator pedaldepression release velocity dθREL on a basis of the following equation(2). In the equation (2), dT denotes a control cycle of this controlprocess in controller 29.

dθREL=(θREL−θCLEAR)/(C _(REL) ×dT)  (2).

[0104] At the next step S35, controller 29 determines if the calculatedaccelerator return velocity dθREL is equal to or higher than theaccelerator return velocity threshold value dθSET.

[0105] If dθREL≧dθSET (Yes) at step S35, the routine goes to a step S36in which the operation enable flag F_(PBS) is set to 1 (F_(PBS)=1).

[0106] At the next step S37, controller 29 updates the presentdepression confirmation flag F_(SET)(n) to the previous depressionconfirmation flag F_(SET)(n−1)and the routine is returned to theoperation determining process shown in FIG. 5.

[0107] On the other hand, if θ≧θCLEAR (No) at step S32, the routinejumps to step S37.

[0108] Furthermore, if, at step S29, F_(OFF)≠1 (No), the routine goes toa step S30. At step S30, the return counter C_(REL) is reset to 0 andthe routine goes to step S37.

[0109] When the subroutine shown in FIG. 6 at step S14 in FIG. 5 isended, the routine goes to a step S15 in FIG. 5.

[0110] At step S15, controller 29 determines if operation enable flagF_(PBS) is set to 1 (F_(PBS)=1).

[0111] If F_(PBS)=1 (yes) at step S15, the routine goes to a step S16.

[0112] At step S16, controller 29 determines if a control operation flagFc is set to 1 and the routine goes to a step S17.

[0113] At step S17, controller 29 determines if the preliminary brakepressure is released. For example, if anyone of conditions such thatbrake pedal 23 has manipulated with the switch signal of brake switch 26in on state to detect that brake pedal 23 has depressed, opening angleof the accelerator pedal 27 is in excess of the depression determiningthreshold value θSET on the basis of accelerator opening angle θ fromaccelerator opening angle sensor 28, or the state wherein thepreliminary brake pressure is developed on the basis of the measuredvalue of time incremental value from a time point at which thedevelopment of the preliminary brake pressure is started and themeasured time has continued equal to or longer than a predetermined timeduration is established, controller 29 determines that it is necessaryto release the development of the preliminary brake pressure.

[0114] If, at step S17, controller 29 determines that it is necessary torelease the development of preliminary brake pressure (Yes), the routinegoes to a step S19 in which the initialization is executed.

[0115] At step S19, control operation flag Fc is reset to 0, the returnstart opening angle θ_(REL) is reset to 0, return counter C_(REL) isreset to 0, return flag F_(OFF) is reset to 0, operation enabling flagF_(PBS) is reset to 0.

[0116] Then, the routine returns to the control process routine shown inFIG. 3.

[0117] On the other hand, if, at step S17,controller 29 determines thatit is not necessary to release the development of the preliminary brakepressure (No), the routine directly returns to the control processroutine shown in FIG. 3.

[0118] In addition, if, at step S15, the operation flag F_(PBS) is not 1(F_(PBS)≠1) (No), the routine goes to step S19 described above.

[0119] It is noted that inter-vehicle distance sensor 31 corresponds tofront object detector to detect the front object to be braked, step S12in FIG. 5 corresponds to detector to detect the vehicular approachingstate, the accelerator opening angle sensor 28 and step S14 in FIG. 5correspond to acceleration/deceleration operation situation detector,steps S13 in FIG. 5 and S15 in FIG. 5 correspond to preliminary brakepressure start determinator, steps S8 through S10 in FIG. 3 correspondto brake pressure developing section, vehicular velocity detector 30corresponds to vehicular velocity detector, and shift position sensor 36correspond to shift position detector.

[0120] Next, an operation of the preview brake controlling apparatus inthe first preferred embodiment will be described below.

[0121] Suppose that the vehicle has stopped with brake pedal 23depressed.

[0122] In this state, in the control procedure in FIG. 3, the routinegoes from step S1 to step S3. Since the vehicle has stopped and thevehicle velocity V is zero, at this time, the routine goes to step S3.At step S3, controller 29 reads the vehicular weight m detected by meansof weight sensor 32. Then, at step S4, controller 29 sets thepreliminary brake pressure to zero. At step S5, power supply toelectromagnetic valve 5 is turned off since preliminary brake pressurePst is zero. Although the preliminary brake pressure Pst is zero, thedriver is depressing brake pedal 23, brake pressure is developed inaccordance with depression variable of brake pedal 23 from mastercylinder 25 so that the vehicle is maintained at stopped state.

[0123] Suppose that brake pedal 23 is released from the stopped stateand the driver depresses accelerator pedal 27 to start the vehicle.

[0124] In this vehicular running state, when the preceding vehicle isnot present or the inter-vehicle distance to the preceding vehicle issufficient not to require the brake, the routine shown in FIG. 3 goesfrom step S1 to step S6 to execute preliminary brake pressuredetermining procedure shown in FIG. 5.

[0125] Then, controller 29 reads the vehicular velocity V and theinter-vehicle distance L(n) and calculates the vehicular velocity dV.Then, controller 29 calculates the determining distance L0 to determinewhether the vehicle is approaching to the object in accordance withequation (1) on the basis of read values (steps S11 and S12).

[0126] At this time, since the preceding vehicle is not present or theinter-vehicle distance L to the preceding vehicle is sufficiently long,L(n)≧L0 at step S13. Since the inter-vehicle distance is not approachingstate, the routine goes to step S19 at which Fc=0.

[0127] Hence, returning to FIG. 3, since Fc=0 and it is not necessary todevelop the preliminary brake pressure at step S7, the routine goes tostep S4.

[0128] At step S4, preliminary brake pressure Pst is set to zero and nopower supply to electromagnetic valve 5 is continued.

[0129] In this running state, suppose that the inter-vehicle distance Lbecomes shorter than the approaching distance L0 due to the follow up toa preceding vehicle whose velocity is shorter than the vehicularvelocity V or the decelerating preceding vehicle. In the process shownin FIG. 5, the routine goes from step S13 to step S14 and the operationdetermining process is executed on the basis of operation situation ofaccelerator pedal 27.

[0130] In the operation determining process of FIG. 6, controller 29sets depression determining threshold value θSET from depressionthreshold value calculation map shown in FIG. 7 on the basis ofvehicular velocity V and shift position of automatic transmission AT.Then, as shown at a time point t0 of FIG. 10A, if the accelerator pedalopening angle θ is narrower than depression determining threshold valueθSET, the routine goes from step S22 to step S25. Then, as shown in FIG.10B, depression flag F_(SET)(n) is set to zero (F_(SET)(n)=0).

[0131] The, if depression flag F_(SET)(n) is continued to zero, theroutine goes from step S26 to step S29. At this time, since return flagF_(OFF) is zero (F_(OFF)=0) (refer to FIG. 10B), the routine goes tostep S30 at which C_(REL)=0 (refer to FIG. 10D).

[0132] Then, the present depression flag F_(SET)(n) is updated to theprevious depression flag F_(SET)(n−1) and the routine returns topreliminary brake pressure determining process shown in FIG. 5.

[0133] At this time, since operation enabling flag F_(PBS) is set tozero (F_(PBS)=0), the routine goes from step S15 to step S19. Then,control operation flag Fc is set to zero (Fc=0).

[0134] Hence, the routine shown in FIG. 3 goes from step S7 to step S4to set preliminary brake pressure Pst to zero and goes to step S5. SincePst is already set to zero, no power supply to electromagnetic valve 5is maintained.

[0135] From this state, when accelerator pedal 27 is further depresseddeeply and opening angle θ of accelerator pedal 27 is in excess ofdepression determining threshold value of θSET at a time point of t1shown in FIGS. 10A through 10D, the routine shown in FIG. 6 goes fromstep S22 to step S23 so that F_(SET)(n)=1 and goes to step S24 in whichθREL=0, C_(REL)=0, F_(OFF)=0, and F_(PBS)=0.

[0136] Since F_(SET)(n−1)=0 and F_(SET)(n)=1, the routine goes from stepS26 to steps S29 and S30 and goes to step S37 in which the presentdepression flag F(n) is updated as previous depression flag F(n−1)(F(n−1))=1). Hence, since operation enabling flag F_(PBS) is maintainedat zero, preliminary brake pressure Pst is set at zero and no powersupply to electromagnetic valve 5 is maintained.

[0137] From this state, when the driver returns the depression stateslowly to become lower than depression determining threshold value θSETat a time point t2, the routine goes from step S22 to step S25.

[0138] Since the routine goes from step S22 to step S25, depression flagF_(SET)(n) is set to zero (F_(SET)(n)=0).

[0139] Since F_(SET)(n−1)=1 and F_(SET)(n)=0, the routine goes from stepS26 to step S27 in which F_(OFF)=0 and the return start opening angleθREL is set to present accelerator opening angle θ (θREL=θ).

[0140] Then, at step S28, accelerator returning velocity threshold valuedθSET is set from the vehicular velocity V of vehicular velocity sensor30 and accelerator returning velocity threshold value dθSET is set fromthe vehicular velocity V of vehicular velocity sensor 30 and acceleratorreturning velocity threshold value dθSET of FIG. 9. This acceleratorreturning velocity threshold value dθSET is set to a relatively largevalue as the vehicular velocity V becomes slower. As the vehicularvelocity V becomes higher, the threshold value of dθSET is set to arelatively small value.

[0141] Next, the routine goes to step S29. Since returning flag F_(OFF)is set to 1 (F_(OFF)=1), the routine goes to step S31 at which thereturn counter C_(REL) is incremented by one (C_(REL)=C_(REL)+1).

[0142] Since, at this time point, the opening angle θ of acceleratorpedal 27 is wider than returning opening angle threshold value θCLEAR.Hence, the routine goes from step S332 to step S37 in which presentdepression flag F_(SET) is maintained to be zero, the preliminary brakepressure Pst is set to be zero and no power supply to electromagneticvalve 5 is maintained at zero.

[0143] While acceleration opening angle θ is narrower than depressiondetermining threshold value θSET and is wider than returning openingangle threshold value θCLEAR , the same processing as described above isrepeated and, at step S31, returning counter C_(REL) is incremented byone.

[0144] At a time point t3, if accelerator pedal opening angle θ becomesnarrower than returning opening angle threshold value θCLEAR, theroutine goes from step S32 to step S33.

[0145] At step S33, F_(OFF) is set to zero (F_(OFF)=0).

[0146] At step S34, controller 29 calculates accelerator pedaldepression returning velocity dθREL on the basis of equation (2).

[0147] In details, controller 29 calculates variation rate Δθ ofaccelerator pedal depression opening angle θ per time duration ΔTbetween time points t2 and t3.

[0148] Then, if accelerator returning velocity dθREL is in excess ofaccelerator returning velocity threshold value dθSET set on the basis ofvehicular velocity V at step S28, namely, the velocity for the driver toreturn accelerator pedal 27 toward release position is accelerator pedalreturning velocity threshold value dθSET, the routine goes from step S35to step S36. At step S36, operation enabling flag F_(PBS) is set to 1(F_(PBS)=1).

[0149] At step S37, present depression flag F(n) is updated as previousdepression flag F_(SET)(n−1).

[0150] Since operation enabling flag F_(PBS) is set to 1 (F_(PBS)=1),the routine goes from step S15 in FIG. 5 to step S16 at which operationcontrol flag Fc is set to 1 (Fc=1).

[0151] At step S17, controller 29 determines if preliminary brakepressure Pst should be released.

[0152] For example, controller 29 determines whether the switch signalof brake switch 28 is turned off to indicate that brake pedal 23 isreleased, and/or accelerator opening angle θ is in excess of depressiondetermining threshold value θSET.

[0153] If controller 29 determines that it is not necessary to releasedevelopment of preliminary brake pressure, the routine goes from stepS17 to step S7 shown in FIG. 3.

[0154] Since, at this time, Fc=1, the routine goes to step S8.Controller 29 then reads vehicular velocity V at which preliminary brakepressure Pst is started. The preliminary brake pressure Pst is set onthe basis of vehicular weight m read when the vehicle stops andvehicular velocity V thereat.

[0155] Next, at step S10, controller 29 reads preliminary brake pressurePb detected by brake pressure sensor 33 and controls a power supply toelectromagnetic valve 5 so as to make the read brake pressure Pbcoincide with the set preliminary brake pressure Pst.

[0156] Therefore, since vacuum valve 3 is closed due to the variationpressure chamber 1 of vacuum booster 24 and, on the contrary,atmospheric pressure valve 4 is opened, the atmospheric pressure valve 4is opened, the atmospheric pressure is introduced into pressurevariation chamber 1 of vacuum booster 24. Hence, the axial envelope 17is moved in the leftward direction so that the push rod 8 is moved inthe leftward direction. Hence, prior to the driver's brake manipulation,brake pressure in accordance with preliminary brake pressure Pst isdeveloped to be braked.

[0157] At this time, the preliminary brake pressure Pst becomes smalleras the vehicular velocity V becomes lower and becomes larger asvehicular weight m becomes heavier. Therefore, preliminary brakepressure Pst becomes small in a case where the number of vehicularoccupants and actually mounted matters are small and vehicular weight mis small at the low velocity region. Consequently, no unpleasant feelingis given to driver even though the vehicle falls in the brake state dueto the brake pressure Pst so that the previous brake control predictingthe brake manipulation by the driver can be achieved.

[0158] At this time, since preliminary brake pressure Pst is developedwhen the driver's depression state of accelerator pedal 27 and itsreturning velocity are in excess of their threshold values, preliminarybrake pressure is acted upon the vehicle at the same time when theengine brake is acted upon the vehicle. Hence, even if the braking forcedue to preliminary brake pressure is acted upon the vehicle with theengine brake also acted upon the vehicle, the sudden application ofbrake to the vehicle body and unpleasant feeling are relieved caused bythe action of braking force by the preliminary brake pressure Pst.

[0159] When in a state where the braking force in accordance withpreliminary brake pressure Pst is developed, the driver depresses brakepedal 23 in place of accelerator pedal 23 in place of accelerator pedal27. Since brake switch 26 detects the depression of brake pedal 23, theroutine shown in FIG. 3 goes from step S1 to step S2. Since the vehicleis running and the vehicular velocity V is V>0, the routine goes to stepS4.

[0160] Since preliminary brake pressure Pst is set to zero and no powersupply to electromagnetic valve 5 is carried out, preliminary brakepressure actually developed in master cylinder 25 gives zero. In placeof it, depression of brake pedal 23 causes brake pressure to bedeveloped in accordance with the depression depth of brake pedal 23.

[0161] At this time, since preliminary brake pressure is developedbefore depression of brake pedal 23 by driver and brake pressure causedby the driver depression on brake pedal 23 is subsequently developed,the responsive characteristic of braking can be improved and shorteningof the free running distance so as to shorten the brake distance can beachieved.

[0162] In addition, since, in the depression determining threshold valuecalculation map in FIG. 7, the depression determining threshold valueθSET which is a criterion of whether the development of preliminarybrake pressure should be started is set to be larger (wider) as thevehicular velocity V becomes low and the engine brake becomes smallerand as the shift position of automatic transmission AT becomes higherand engine brake becomes smaller. Hence, depression determiningthreshold value θSET is set in accordance with the magnitude of theengine brake actually developed. Consequently, a more accurate avoidanceof unpleasant feeling to the driver can be achieved.

[0163] In addition, since depression determining threshold value θSET isset to be large in the low velocity region in which the engine brakecannot be expected and is set to develop the preliminary brake pressurewhen the vehicle is in such an acceleration state that a sufficientengine braking can be obtained, the same advantage as the high velocitycan be achieved even when the vehicular velocity V is low.

[0164] Furthermore, in the accelerator returning velocity thresholdvalue calculation map shown in FIG. 9, the accelerator returningvelocity threshold value dθSET which is a criterion of determiningwhether the preliminary brake pressure development should be started isset to be smaller as the vehicular velocity V becomes higher.

[0165] Hence, although the vehicular brake distance is extended as thevehicular velocity V becomes increased, the preliminary brake pressureis developed at earlier stage in accordance with the acceleratorreturning velocity. Consequently, an effective development ofpreliminary brake pressure can be achieved and the vehicular brakedistance can be shortened.

[0166] On the other hand, from a state where the braking force inaccordance with preliminary brake pressure Pst is developed to a statewhere the driver depresses again the accelerator pedal 27 so that theopening angle θ is in excess of accelerator depression determiningthreshold value θSET, namely, the driver depresses again acceleratorpedal 27 after the depression of accelerator pedal 27 is released, thisis detected at step S17 in FIG. 5 and the routine goes from step S17 tostep S19 in which the control operation flag Fc is set to zero. Hence,the routine shown in FIG. 3 goes from step S7 to step S4 so that thepreliminary brake pressure Pst is set to zero to release the developmentof preliminary brake pressure Pst.

[0167] In the same manner as described above, when the state where thebraking force in accordance with the preliminary brake pressure Pst iscontinued for a preset reference time duration or longer, namely, whenthe state where the depression of accelerator pedal 27 is released forthe present reference time duration or longer, or when the depression ofbrake pedal 23 is not carried out, this is detected at step S17 shown inFIG. 5 and the routine goes from step S17 to step S19 so that controloperation flag Fc is set to zero. At this time, the development ofpreliminary brake pressure is released. Hence, at a time point at whichthe transfer to the depression of brake pedal is not expected to becarried out, the preliminary brake pressure is released so that theunnecessary development of preliminary brake pressure Pst can beavoided.

[0168] The above-described reference time duration is, for example,approximately 1 second.

[0169] It is noted that, in the first embodiment, even if theinter-vehicle distance L(n) is shorter than approaching distance L0,preliminary brake pressure is not developed when, in the operationdetermining process, the accelerator opening angle θ is not in excess ofdepression determining threshold value θSET or accelerator returningvelocity dθSET if the accelerator opening angle θ is in excess ofdepression determining threshold value θSET. The fact that acceleratorreturning velocity dθREL is not in excess of accelerator returningvelocity threshold value dθSET means that a manner that returningaccelerator pedal 27 is relatively moderate and can be deemed that animmediate transfer to the depression of brake pedal 23 does not occur.Hence, no problem occurs without development of preliminary brakepressure.

[0170] It is further noted that depression determining threshold valueθSET is set in accordance with vehicular velocity V. When the vehicularvelocity V is high, depression determining threshold value θSET is setto the relatively small (narrow) value. On the contrary, when thevehicular velocity V is low, the depression determining threshold valueθSET is set to the relatively small value (narrow value). On thecontrary, when the vehicular velocity V is low, depression determiningthreshold value θSET is set to the relatively large (wide) value.

[0171] If accelerator opening angle θ is not in excess of depressiondetermining threshold value θSET, preliminary brake pressure is notdeveloped. However, when the vehicular velocity V is relatively low, thevehicle can relatively quickly be stopped when the driver depressesbrake pedal 23, When, in this case, accelerator opening angle θ isnarrower than depression determining threshold value θSET under therelatively high vehicular velocity V, this means that the vehicle is notso accelerated. From this state, when accelerator pedal 27 is released,a relatively strong engine brake occurs so that the relativelysufficient braking force is secured. This case raises no problem.

[0172] (Second Embodiment)

[0173] Next, a second preferred embodiment of the preview brakecontrolling apparatus according to the present invention will bedescribed below.

[0174]FIG. 11 shows a circuit block diagram of the preview brakecontrolling apparatus in the second embodiment.

[0175] As shown in FIG. 11, an acceleration sensor 35 to detect avehicular acceleration acted upon the vehicle is added to the structureshown in FIG. 1A of the first embodiment.

[0176] The acceleration G detected by the acceleration sensor 35 isinputted to controller 29.

[0177] Controller 29 in the second embodiment executes the controlprocedure shown in FIG. 3 and preliminary brake pressure determiningprocess shown in FIG. 5 in the same manner as described in the firstembodiment.

[0178] However, at operation determining process based on themanipulation of accelerator pedal 27 at step S14, another operationdetermining procedure shown in FIG. 12 is executed on a basis ofacceleration G from acceleration sensor 35. It is noted that since thesame reference numerals designate corresponding like elements describedin the first embodiment of FIG. 6, detailed explanation thereof willherein be omitted.

[0179] In details, at step S21 a, controller 29 sets depressiondetermining threshold value G_(SET) to detect a development situation ofvehicular acceleration.

[0180] This setting of depression determining threshold value G_(SET) iscarried out by, for example, referring to a calculation map of thedepression determining threshold value shown in FIG. 13 on the basis ofthe vehicular velocity V detected by the vehicular velocity sensor 30.

[0181]FIG. 13 shows the depression determining calculation maprepresenting a relationship between the vehicular velocity V anddepression determining threshold value G_(SET).

[0182] The depression determining threshold value G_(SET) is set to avalue which can be deemed not to give the driver the sudden applicationof brake or unpleasant feeling even when the preliminary brake pressureis applied to some degree to the vehicle body in a case where the enginebrake is acted upon the vehicle body with accelerator pedal 27 releasedfrom a state where the accelerator pedal 27 is depressed to develop anacceleration on the vehicle body, in the same way as the case of thedepression determining threshold value θSET in the first embodiment.

[0183] In details, as shown in FIG. 13, the characteristic curve is setto have the constant maximum value Gmax at the relatively low vehicularvelocity region D1 which is equal to or below the city street runningvelocity (approximately 40 Km/h), to have the constant minimum valueGmin at the relatively high vehicular velocity region D3 which is equalto or higher than free-way vehicular running velocity (approximately 80Km/h), and is set to take the linear interpolation value between maximumand minimum values Gmax and Gmin at the intermediate running velocityregion D2.

[0184] If the depression determining threshold value GSET is set at stepS21 a, the routine shown in FIG. 12 goes to a step S22 a.

[0185] At step S22 a, controller 29 determines if the magnitude ofacceleration G detected by the acceleration sensor 35 is larger than thedepression determining threshold value G_(SET).

[0186] If G≦G_(SET) (No), the routine goes to step S25.

[0187] At step S25, controller 29 sets present depression flagF_(SET)(n) to zero (F_(SET)(n)=0) and the routine goes to step S26.

[0188] If previous depression flag F_(SET)(n−1) is zero(F_(SET)(n−1)=0), the routine goes from step S26 to step S29 sincepresent depression flag F_(SET)(n)=0.

[0189] At this time, return flag F_(OFF) is zero (F_(OFF)=0), theroutine goes to step S30 in which counter C_(REL) is updated asC_(REL)=0 and the routine goes to step S37 in which present depressionflag F_(SET)(n) is updated as previous depression flag F_(SET)(n−1).Then, the routine shown in FIG. 12 is ended and returns to the operationdetermining process in FIG. 5.

[0190] In this case, since operation enabling flag F_(PBS) is F_(PBS)=0,preliminary brake pressure Pst is not developed.

[0191] From this case, if the acceleration G is increased and is inexcess of the depression determining threshold value G_(SET), theroutine shown in FIG. 12 goes from step S22 a to a step S23 in whichdepression flag F_(SET)(n) is updated as F_(SET) to 1. Then, at a stepS24 a, the initialization is carried out.

[0192] At step S24 a, a return start acceleration G_(REL) is zeroed(G_(REL)=0), return counter is zeroed (C_(REL)=0), return flag F_(OFF)is zeroed (F_(OFF)=0), and operation enabling flag F_(PBS) is zeroed.

[0193] Then, the routine goes to a step S26.

[0194] Since, at this time, previous depression flag F_(SET)(n−1) iszeroed, the routine goes to step S29. Then, the routine goes to step S37via step S30.

[0195] Thus, in this case, no preliminary brake pressure is developed.

[0196] From this state, the driver returns the depressed acceleratorpedal 27 to decrease the acceleration G and the acceleration G is belowthe depression determining threshold value G_(SET). At this time, theroutine goes from step S22 a to step S25 in which the depression flagF_(SET)(n) is updated to zero. Since, at step S26, the previousdepression flag F_(SET)(n−1) is 1 and present depression flag F_(SET)(n)is zero, the routine goes to a step S27 a.

[0197] At step S27 a, return flag F_(OFF) is set to 1 (F_(OFF)=1) andreturn start acceleration G_(REL) is set to G (G_(REL)=G). Then, theroutine goes to a step S28 a.

[0198] At step S28 a, an acceleration variation rate threshold valuedG_(SET) is set from an acceleration variation rate threshold valuecalculation map and the vehicular velocity V of the vehicular velocitysensor 30.

[0199] The acceleration variation rate threshold value calculation maprepresents the relationship between the vehicular velocity V and theacceleration variation rate threshold value dG_(SET).

[0200] The acceleration variation rate threshold value dG_(SET) isgenerally the same as the accelerator returning velocity threshold valuedθSET described in the first embodiment with reference to theaccelerator returning velocity threshold value calculation map shown inFIG. 9 and is set to a value which can predict that the deriver releasesthe accelerator pedal 27 and depresses brake pedal 23.

[0201] The characteristic curve of the acceleration variation ratethreshold value dG_(SET) is set to have the constant maximum value Gmaxat the low velocity region which is equal to or lower than the citystreet running vehicular velocity (approximately 40 Km/h), is set tohave the constant minimum value Gmin at the high velocity region whichis equal to or higher than the free-way running vehicular velocity(approximately 80 Km/h), and is set to have the linear interpolationvalue between the maximum and minimum values Gmax and Gmin at the middlevehicular velocity region.

[0202] Then, if, at step S28 a, controller 29 sets the accelerationvariation rate dG_(SET), the routine goes to step S28 a. Since returnflag F_(OFF) is 1 (F_(OFF)=1), the routine goes from step S29 to stepS31 in which return counter C_(REL) is incremented by one.

[0203] At step S32 a, controller 29 determines if the acceleration G issmaller than a preset return opening angle threshold value G_(CLEAR) bywhich the accelerator pedal 27 can be deemed to be released.

[0204] If G is smaller than G_(CLEAR), viz., while the acceleration issuch that the accelerator pedal cannot be deemed to be released, theroutine goes from a step S32 a to step S37. Hence, since operationenabling flag F_(PBS) is maintained at zero (F_(PBS)=0), no preliminarypressure is developed.

[0205] Then, if the depressed accelerator pedal 27 is relieved andacceleration G becomes smaller than return opening angle threshold valueG_(CLEAR), the controller 29 determines that accelerator pedal 27 hasbeen released and the routine goes from step S32 a to step S33.

[0206] After return flag F_(OFF) is zeroed (F_(OFF)=0), the routine goesto a step S34 a.

[0207] At step S34 a, controller 29 calculates an acceleration variationrate dG_(REL) on the basis of the following equation (3).

dG _(REL)=(G _(REL) −G _(CLEAR))/(C _(REL) ×dT)  (3).

[0208] At the next step S35 a, controller 29 determines whether theacceleration variation rate dG_(REL) is equal to or larger thanacceleration variation rate threshold value dG_(REL)(dG_(REL)≧dG_(SET)).

[0209] If dG_(REL)≧dG_(SET) (Yes) at step S35 a, namely, if it ispredicted that the variation rate of acceleration is so large that thedriver releases accelerator pedal 27 and driver's driving is transferredto the depression of brake pedal 23, the routine goes to a step S36.

[0210] At step S36, operation enabling flag F_(PBS) is set to 1(F_(PBS)=1), the routine goes to step S37 in which present depressionflag F_(SET)(n) is updated as previous depression flag F_(SET)(n−1) andthe routine returns to operation determining procedure shown in FIG. 5.

[0211] Since operation enabling flag F_(PBS) is set to 1 (F_(PBS)=1),operation control flag Fc (Fc=1) at step S16 shown in FIG. 5 is set to 1(Fc=1). Thus, at control procedure shown in FIG. 3, the routine goesfrom step S7 to step S8.

[0212] In the same manner as described above, preliminary brake pressurePst is set on the basis of vehicular velocity V so that electromagneticvalve 5 is controlled to make brake pressure Pb coincident withpreliminary brake pressure Pst.

[0213] On the other hand, if acceleration variation rate dG_(REL) issmaller than acceleration variation rate threshold value dG_(SET),namely, if it cannot be predicted that the driver depresses brake pedal23, the routine goes directly from step S25 a to step S37. Hence, sinceoperation enabling flag F_(PBS) maintains at zero (F_(PBS)=0), nodevelopment of preliminary brake pressure is carried out.

[0214] Hence, the same advantages as the first embodiment can beachieved in the second embodiment.

[0215] The acceleration sensor 35 is newly installed in the secondembodiment to detect a vehicular acceleration. For example, variationrate in the vehicular velocity V is calculated and this may be used asvehicular acceleration G.

[0216] In each of the first and second embodiments, preliminary brakepressure Pst is set on the basis of vehicular velocity V and vehicularweight m. However, vehicular deceleration maybe detected and preliminarybrake pressure Pst may be set on the basis of vehicular velocity V andvehicular weight m.

[0217] As vehicular weight m becomes larger, preliminary brake pressurePst becomes larger. As vehicular deceleration becomes larger,preliminary brake pressure Pst may become smaller.

[0218] In addition, preliminary brake pressure Pst may be set to becomesmaller in accordance with smaller road surface friction coefficientwhile detecting road surface state.

[0219] In each of the first and second embodiments, accelerator openingangle sensor or acceleration sensor applied as acceleration/decelerationoperation situation detector. For example, controller 29 may determinethe required preliminary brake pressure state when the shift position ofautomatic transmission AT is transferred from an overdrive position to ashifted down position.

[0220] In each of the first and second preferred embodiments, brakeoperation situation is detected on the basis of the state of brakeswitch 26.

[0221] However, the brake operation situation may be detected from astroke of brake pedal 23 or a start of brake operation may be detectedwhen the brake pressure Pb detected by the brake pressure sensor 33 isequal to or higher than preliminary brake pressure Pst.

[0222] In each of the first and second embodiments, the precedingvehicle is detected by inter-vehicle distance sensor 31. However, evenif an obstacle such as dropped obstacle on a road surface on which thevehicle is to run which is required for the driver to manipulate brakeis detected, this may detect inter-vehicle distance sensor 31. In thesame manner as described above, the preview brake control may be carriedout.

[0223] In each of the first and second preferred embodiments, thecalculation of relative velocity to the front obstacle is carried out.However, in a case where the inter-vehicle distance sensor which canalso detect the relative velocity is applied, the detected relativevelocity may directly be used.

[0224] In each of the first and second embodiments, the electromagneticvalve 5 is incorporated into vacuum booster 24 so that brake pressure Pbin accordance with preliminary brake pressure Pst is developed.

[0225] However, such a fluid pressure source as an oil pump may bedisposed, a fluid pressure of this fluid pressure source is pressurecontrolled with a pressure control valve to develop a preliminary brakepressure Pst, and this pressure may be supplied to a brake actuator.

[0226] In each of the first and second preferred embodiments, mastercylinder 25 is used to develop the brake pressure. However, an electricmotor may be used as the brake actuator to develop the braking force. Inthis case, a drive current to the motor may be controlled on the basisof preliminary brake pressure Pst.

[0227] It is noted that the brake pre-pressure described in the drawingscorrespond to the preliminary brake pressure Pst.

[0228] The entire contents of Japanese Patent Applications No.2000-043396 filed in Japan on Feb. 21, 2000 are herein incorporated byreference. Although the invention has been described above by referenceto certain embodiment of the invention, the invention is not limited tothe embodiments described above. Modifications and variations of theembodiments described above will occur to those skilled in the art inthe light of the above teachings.

[0229] The scope of the invention is defined with reference to thefollowing claims.

What is claimed is:
 1. A preview brake controlling apparatus for anautomotive vehicle, comprising: an object detector to detect a relativedistance of the vehicle to an object for the vehicle to be braked; anapproaching state detector to detect whether the vehicle is approachingto the object on the basis of the relative distance of the vehicle tothe object; a vehicular velocity variation rate manipulation situationdetector to detect a manipulation situation on a vehicular velocityvariation rate; a preliminary brake pressure application startdetermining section that determines whether the vehicle falls in apreliminary brake pressure application enabled state requiring apreliminary brake pressure application on the basis of detection resultsby the approaching state detector and by the vehicular velocityvariation rate manipulation situation detector; and a brake pressuregenerator to develop a predetermined minute brake pressure in accordancewith a vehicular running condition prior to a vehicular driver's brakemanipulation when the preliminary brake pressure application startdetermining section determines that the vehicle falls in the preliminarybrake pressure application enabled state.
 2. A preview brake controllingapparatus for an automotive vehicle as claimed in claim 1 , wherein thepreliminary brake pressure application state determining sectiondetermines that the vehicle falls in the preliminary brake pressureapplication enabled state when the approaching state detector detectsthat the vehicle is approaching to the object and when the vehicularvelocity variation rate manipulation detector detects that such adeceleration manipulation as to exceed an accelerator release velocitythreshold value is carried out.
 3. A preview brake controlling apparatusfor an automotive vehicle as claimed in claim 1 , wherein thepreliminary brake pressure application state determining sectiondetermines that the vehicle falls in the preliminary brake pressureapplication enabled state when the approaching state detector detectsthat the vehicle is approaching to the object and when the vehicularvelocity variation rate manipulation situation detector detects that adeceleration manipulation is carried out from a state in which anaccelerator manipulated variable detected by the vehicular velocityvariation rate manipulation situation detector has exceeded anacceleration manipulated variable threshold value.
 4. A preview brakecontrolling apparatus for an automotive vehicle as claimed in claim 1 ,wherein the preliminary brake pressure application state determiningsection determines that the vehicle falls in the preliminary brakepressure application enabled state when the approaching state detectordetects that the vehicle is approaching to the object and when thevehicular velocity variation rate manipulation situation detectordetects that a deceleration manipulation is carried out from a state inwhich an acceleration manipulated variable detected by the vehicularvelocity variation rate manipulation situation detector has exceeded anacceleration manipulated variable threshold value and that a velocity ofthe deceleration manipulation has exceeded an accelerator releasevelocity threshold value.
 5. A preview brake controlling apparatus foran automotive vehicle as claimed in claim 2 , wherein the decelerationmanipulation release velocity threshold value is set on the basis of avehicular velocity of the vehicle and the preliminary brake pressureapplication start determining section comprises a vehicular velocitydetector to detect a vehicular velocity of the vehicle, and thedeceleration manipulation release velocity threshold value is set loweras the vehicular velocity becomes higher.
 6. A preview brake controllingapparatus for an automotive vehicle as claimed in claim 3 , wherein theacceleration manipulated variable threshold value is set on the basis ofa vehicular velocity of the vehicle and the preliminary brake pressureapplication start determining section comprises a vehicular velocitydetector to detect the vehicular velocity of the vehicle, and theacceleration manipulated variable threshold value is set smaller as thevehicular velocity becomes higher.
 7. A preview brake controllingapparatus for an automotive vehicle as claimed in claim 3 , wherein theacceleration manipulated variable threshold value is set on the basis ofa vehicular velocity of the vehicle and the preliminary brake pressureapplication start determining section comprises a shift positiondetector to detect a shift position of a transmission of the vehicle,and the acceleration manipulated variable threshold value is set smalleras the shift position of the transmission becomes a lower speed range.8. A preview brake controlling apparatus for an automotive vehicle asclaimed in claim 1 , wherein the vehicular velocity variation ratemanipulation situation detector comprises a detector to detect amanipulated variable of an accelerator pedal.
 9. A preview brakecontrolling apparatus for an automotive vehicle as claimed in claim 1 ,wherein the vehicular velocity variation rate manipulation situationdetector comprises a detector to detect a longitudinal acceleration ofthe vehicle.
 10. A preview brake controlling apparatus for an automotivevehicle as claimed in claim 1 , wherein the vehicular velocity variationrate manipulation situation detector comprises a detector to detect ashift position of a transmission of the vehicle.
 11. A preview brakecontrolling apparatus for an automotive vehicle as claimed in claim 1 ,wherein the preliminary pressure application start determining sectioncomprises a vehicular velocity detector to detect a vehicular velocityof the vehicle and the brake pressure generator determines thepreliminary brake pressure (Pst) from a characteristic table inaccordance with the vehicular velocity of the vehicle at which theapplication of the preliminary brake pressure is started and a vehicularweight which is measured when the vehicle stops.
 12. A preview brakecontrolling apparatus for an automotive vehicle as claimed in claim 1 ,wherein the brake pressure generator generates the predeterminedconstant preliminary brake pressure for a reference time duration.
 13. Apreview brake controlling apparatus for an automotive vehicle as claimedin claim 1 , wherein the brake pressure generator releases thedevelopment of the preliminary brake pressure when an accelerationmanipulated variable detected by the vehicular velocity variation ratemanipulation situation detector has exceeded an acceleration manipulatedvariable threshold value during the development of the preliminary brakepressure.
 14. A preview brake controlling apparatus for an automotivevehicle as claimed in claim 11 , wherein the predetermined preliminarybrake pressure is set to become larger as the vehicular velocity of thevehicle (V0) at which the application of the preliminary brake pressureis started becomes higher and to become larger as the vehicular weightbecomes heavier.
 15. A preview brake controlling apparatus for anautomotive vehicle as claimed in claim 1 , wherein the approaching statedetector detects whether the vehicle is approaching to the object on thebasis of whether the relative distance (L) of the vehicle to the objectis shorter than an approaching distance (L0) based on a relativevelocity of the vehicle to the object and a differential value (dV) ofan inter-vehicle distance from the vehicle to the object.
 16. A previewbrake controlling apparatus for an automotive vehicle as claimed inclaim 1 , wherein the preliminary brake pressure application startdetermining section comprises: an opening angle sensor to detect anopening angle of an accelerator pedal; a deceleration manipulationvelocity calculator (dθREL) on the basis of an accelerator pedal releasestart opening angle (θREL), an accelerator pedal opening angle thresholdvalue (θCLEAR) enabling for the accelerator pedal to be deemed to bereleased, and a time duration for the vehicular driver to release fromthe accelerator pedal; and a comparator to compare the calculatedaccelerator pedal returning velocity (dθREL) is equal to or larger thanthe release velocity threshold value (dθSET); and a control operationflag (Fc) representing that the preliminary brake pressure applicationis enabled and set when the accelerator pedal returning velocity isequal to or larger than the release velocity thresholdvalue(dθREL≧dθSET).
 17. A preview brake controlling apparatus for anautomotive vehicle as claimed in claim 9 , wherein the preliminary brakepressure application start determining section comprises: an openingangle sensor to detect an opening angle of an accelerator pedal and anacceleration variation rate calculator to calculate an accelerationvariation rate (dGEL) on the basis of an accelerator pedal release startopening angle (GREL), an accelerator pedal opening angle threshold value(GCLEAR) enabling for the accelerator pedal to be deemed to be released,and a time duration for the vehicular driver to release from theaccelerator pedal; and a comparator to compare the calculatedaccelerator pedal returning velocity (dGREL) is equal to or larger thanan acceleration variation rate threshold value (dGSET); and a controloperation flag (Fc) representing that the preliminary brake pressureapplication is enabled and set when the accelerator pedal returningvelocity is equal to or larger than the release velocity thresholdvalue(dGREL≧dGSET).
 18. A preview brake controlling method for anautomotive vehicle, comprising: detecting a relative distance of thevehicle to an object for the vehicle to be braked; detecting whether thevehicle is approaching to the object on the basis of the relativedistance of the vehicle to the object; detecting a vehicular velocityvariation rate manipulation situation; determining whether the vehiclefalls in a preliminary brake pressure application enabled staterequiring a preliminary brake pressure application on the basis ofdetection results at the steps of the approaching state detecting and ofthe vehicular velocity variation rate manipulation situation; anddeveloping a predetermined constant brake pressure in accordance with avehicular running condition prior to a vehicular driver's brakemanipulation when determining that the vehicle falls in the brakepreliminary application state.
 19. A preview brake controlling apparatusfor an automotive vehicle, comprising: object detecting means fordetecting a relative distance of the vehicle to an object for thevehicle to be braked; approaching state detecting means for detectingwhether the vehicle is approaching to the object on the basis of therelative distance of the vehicle to the object; vehicular velocityvariation rate manipulation situation detecting means for detecting amanipulation situation on a vehicular velocity variation rate;preliminary brake pressure application start determining means fordetermining whether the vehicle falls in a preliminary brake pressureapplication enabled state requiring a preliminary brake pressureapplication on the basis of detection results by the approaching statedetecting means and by the vehicular velocity variation ratemanipulation situation detecting means; and brake pressure generatingmeans for developing a predetermined minute brake pressure in accordancewith a vehicular running condition prior to a vehicular driver's brakemanipulation when the preliminary brake pressure application startdetermining means determines that the vehicle falls in the preliminarybrake pressure application enabled state.